Method 1: Just turn on the macOS native setting.

Turns out there’s a “hidden” (from me, obviously) setting right in the Keyboard → Text preference pane to “Add period with double-space”.

Duh.

Use that: it’s fast and works just like iOS.

Except when it doesn’t, like in “web app” type apps like Slack or anywhere in Chrome and who knows where else.

Which brings us to method 2…

Method 2: Set up a BetterTouchTool “Custom Key Sequence”

I have used software called BetterTouchTool for small productivity boosts on macOS for years.

It has stupid-configurable window snapping tools, which is why I originally bought it, but it also allows you to allows you to set up custom actions based on mouse or trackpad gestures, gives much finer-grained control over the speed of things like mouse tracking, scrolling, where the touch-sensitive areas of your Magic Mouse are and a million other things.

What I realized this morning was that I can use its custom key sequences to overcome the frustrating lack of being able to hit spacebar twice and get a damn period.